Rockwool Comfortboard 80 vs 110: Which Exterior Insulation Is Right?

A contractor's breakdown of density, R-value, compressive strength, and the real-world applications where each product performs best.

Rockwool makes two rigid mineral wool boards designed for exterior continuous insulation: Comfortboard 80 and Comfortboard 110. Both are non-combustible, vapor-permeable, and hydrophobic. But they are not interchangeable. The density difference between them determines where each one belongs in a wall or roof assembly.

This guide gives you the technical specs, application guidance, and cost analysis you need to spec the right board on your next project.

Quick Comparison: Comfortboard 80 vs 110

The critical takeaway: R-value per inch is identical. You are not buying Comfortboard 110 for better thermal performance. You are buying it for higher compressive strength.

Understanding the Density Difference

Comfortboard 80 has a density of 8 lbs per cubic foot. Comfortboard 110 is 11 lbs per cubic foot — 37.5% denser. That extra mass translates directly into compressive resistance.

At 10% deformation, Comfortboard 80 handles 150 PSF (pounds per square foot). Comfortboard 110 handles 300 PSF. This is not a subtle difference. It is double the compressive strength.

Why does compressive strength matter for insulation? Because exterior insulation carries loads. Cladding attachment screws bear through the insulation. Roof assemblies transfer dead loads and live loads (snow) through the insulation layer. Under slabs, the full weight of the concrete and everything above it presses down on the insulation.

When to Use Comfortboard 80

Comfortboard 80 is the standard choice for exterior wall insulation in residential and light commercial construction. It handles the compressive loads typical of wall applications without issue.

Ideal Applications

• Exterior walls over sheathing: The most common application. Comfortboard 80 installs over OSB or plywood sheathing, under a rainscreen cavity and cladding. At 2" thickness, it provides R-8 of continuous insulation — enough to meet the 2021 IRC climate zone 5 requirement for R-7.5 CI.
• Wood-frame walls up to 3 stories: The compressive strength is adequate for standard cladding attachments using screws through the insulation into studs or sheathing.
• Above-grade foundation walls: Comfortboard 80 at 2" or 3" over a foundation wall (above the soil line) adds continuous insulation and provides drainage.
• Interior sound attenuation: While designed for exterior use, Comfortboard 80 also works as a dense, rigid acoustic panel for interior partition walls, media rooms, and mechanical room isolation.

When to Use Comfortboard 110

Comfortboard 110 is engineered for high-compression applications where 80 would deform over time. If there is sustained weight pressing on the insulation, you need 110.

Ideal Applications

• Low-slope and flat roofing: Roof insulation carries the dead load of the membrane, any ballast or pavers, and live loads from snow and maintenance traffic. In Canadian climate zones 6 and 7, snow loads of 40 to 60 PSF are common. Comfortboard 110 at 300 PSF capacity handles this with ample safety factor.
• Under concrete slabs: Basement slabs and heated garage floors. The full weight of the slab (typically 12.5 PSF per inch of thickness) plus live loads sits on the insulation permanently. Comfortboard 110 resists this sustained compression without creep.
• Plaza decks and green roofs: Pavers, soil, and vegetation add significant dead loads. Only Comfortboard 110 (or higher-density products) can handle these loads over a 30+ year service life.
• Heavy cladding systems: Brick veneer, stone veneer, and precast panels create concentrated loads at anchor points. Comfortboard 110 resists point-load compression better than 80.
• Below-grade foundation walls: Where the insulation must resist lateral soil pressure in addition to compression. Comfortboard 110's density resists deformation from backfill pressure.

R-Value by Thickness: Both Products

Comfortboard 80 delivers R-4.2 per inch and Comfortboard 110 delivers R-4.3 per inch, the R-value depends solely on thickness:

Installation Methods

Mechanical Fastening (Walls)

Both Comfortboard products install the same way on exterior walls. The board is held against the sheathing with long screws and insulation washers (Rodenhouse or equivalent) that penetrate through the insulation into the studs or structural sheathing.

• Fastener: #10 or #12 wood screws, length = insulation thickness + 1.5" minimum penetration into framing
• Washer: 2" to 3" diameter plastic insulation retainers
• Pattern: One fastener per 2 square feet minimum, with additional fasteners at board edges and corners
• Joints: Butt joints, staggered from sheathing joints. No tape required at Comfortboard joints (the material is vapor-open, and the air barrier is at the sheathing layer).

Adhered Systems (Walls)

Some EIFS and stucco systems use adhesive to bond Comfortboard directly to the sheathing. Use a mineral-wool-compatible adhesive (not foam adhesive). Mechanical fasteners are still recommended as supplemental attachment, especially on walls taller than one story.

Roof Installation

On flat roofs, Comfortboard 110 is laid in one or two layers over the roof deck, with the membrane system installed on top. Boards are typically loose-laid and held in place by the membrane and ballast. For mechanically attached membranes, the fasteners penetrate through the insulation into the deck. Consult the membrane manufacturer's approved fastener schedule.

Cost Comparison and When the Premium Is Justified

Comfortboard 110 costs approximately 30% to 40% more than Comfortboard 80 at equivalent thickness. For a 2" board, expect to pay $38 to $48 for 110 versus $28 to $35 for 80 (prices vary by region and volume).

On a typical 2,000 sq ft house with approximately 2,800 sq ft of exterior wall area, choosing Comfortboard 80 at 2" thickness costs roughly $2,000 to $2,500 in material. Upgrading to 110 for the same walls would add $700 to $1,000. That premium is not justified for standard wall applications where 80 meets the compressive requirements.

However, on a 1,500 sq ft flat roof with a 50 PSF snow load and a ballasted membrane, Comfortboard 110 is not optional — it is required. Using 80 in that application risks long-term compression creep and insulation failure.

Fire Performance

Both products are non-combustible and carry a fire resistance rating to 1,177 degrees F. This is a significant advantage over foam insulations (EPS, XPS, polyiso) in fire-sensitive applications:

• No ignition barrier required under most building codes
• Meets NFPA 285 requirements for exterior wall assemblies in buildings over 40 feet
• No toxic smoke or dripping when exposed to flame
• Qualifies as a thermal barrier for spray foam underneath (in hybrid assemblies)

For mid-rise wood-frame construction (Type V-A) where exterior insulation must be non-combustible per IBC Section 2603, mineral wool boards are often the only practical option that also provides the required R-value.

Moisture Management

Both Comfortboard products have water vapor permeance above 30 perms at 1" thickness. This is critical. Mineral wool insulation allows the wall assembly to dry outward through the insulation layer. Foam insulations (particularly XPS at under 1 perm for 2") trap moisture inside the wall cavity.

Rockwool is also hydrophobic — the fibers are treated to repel liquid water. If bulk water gets behind the cladding (and it will), mineral wool drains freely and dries quickly. Foam boards absorb water over time, losing R-value and creating conditions for mold growth on the sheathing.

Making the Decision: 80 or 110?

The decision tree is straightforward:

1. Is the insulation on a vertical wall with standard cladding? Use Comfortboard 80.
2. Is the insulation on a roof, under a slab, or under heavy cladding? Use Comfortboard 110.
3. Is the insulation below grade, resisting soil pressure? Use Comfortboard 110.
4. Are you unsure about the loads? Use Comfortboard 110. The cost premium is modest insurance against long-term compression failure.